• Meagan P O'Brien, Eduardo Forleo-Neto, Bret J Musser, Flonza Isa, Kuo-Chen Chan, Neena Sarkar, Katharine J Bar, Ruanne V Barnabas, Dan H Barouch, Myron S Cohen, Christopher B Hurt, Dale R Burwen, Mary A Marovich, Peijie Hou, Ingeborg Heirman, John D Davis, Kenneth C Turner, Divya Ramesh, Adnan Mahmood, Andrea T Hooper, Jennifer D Hamilton, Yunji Kim, Lisa A Purcell, Alina Baum, Christos A Kyratsous, James Krainson, Richard Perez-Perez, Rizwana Mohseni, Bari Kowal, A Thomas DiCioccio, Neil Stahl, Leah Lipsich, Ned Braunstein, Gary Herman, George D Yancopoulos, David M Weinreich, and Covid-19 Phase 3 Prevention Trial Team.
• From Regeneron Pharmaceuticals, Tarrytown, NY (M.P.O., E.F.-N., B.J.M., F.I., K.-C.C., N. Sarkar, P.H., I.H., J.D.D., K.C.T., D.R., A.M., A.T.H., J.D.H., Y.K., L.A.P., A.B., C.A.K., B.K., A.T.D., N. Stahl, L.L., N.B., G.H., G.D.Y., D.M.W.); the Departments of Medicine and Microbiology, University of Pennsylvania, Philadelphia (K.J.B.); the Departments of Global Health and Epidemiology and the Division of Allergy and Infectious Diseases, University of Washington, and the Vaccine and Infectious Diseases Division, Fred Hutchinson Cancer Research Center - both in Seattle (R.V.B.); the Center for Virology and Vaccine Research, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston (D.H.B.); the Institute for Global Health and Infectious Diseases, University of North Carolina at Chapel Hill, Chapel Hill (M.S.C., C.B.H.); the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD (D.R.B., M.A.M.); Clinical Trials of Florida (J.K.) and Medical Research of Westchester (R.P.-P.) - both in Miami; and the Catalina Research Institute, Montclair, CA (R.M.).
• N. Engl. J. Med. 2021 Sep 23; 385 (13): 118411951184-1195.

BackgroundREGEN-COV (previously known as REGN-COV2), a combination of the monoclonal antibodies casirivimab and imdevimab, has been shown to markedly reduce the risk of hospitalization or death among high-risk persons with coronavirus disease 2019 (Covid-19). Whether subcutaneous REGEN-COV prevents severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and subsequent Covid-19 in persons at high risk for infection because of household exposure to a person with SARS-CoV-2 infection is unknown.MethodsWe randomly assigned, in a 1:1 ratio, participants (≥12 years of age) who were enrolled within 96 hours after a household contact received a diagnosis of SARS-CoV-2 infection to receive a total dose of 1200 mg of REGEN-COV or matching placebo administered by means of subcutaneous injection. At the time of randomization, participants were stratified according to the results of the local diagnostic assay for SARS-CoV-2 and according to age. The primary efficacy end point was the development of symptomatic SARS-CoV-2 infection through day 28 in participants who did not have SARS-CoV-2 infection (as measured by reverse-transcriptase-quantitative polymerase-chain-reaction assay) or previous immunity (seronegativity).ResultsSymptomatic SARS-CoV-2 infection developed in 11 of 753 participants in the REGEN-COV group (1.5%) and in 59 of 752 participants in the placebo group (7.8%) (relative risk reduction [1 minus the relative risk], 81.4%; P<0.001). In weeks 2 to 4, a total of 2 of 753 participants in the REGEN-COV group (0.3%) and 27 of 752 participants in the placebo group (3.6%) had symptomatic SARS-CoV-2 infection (relative risk reduction, 92.6%). REGEN-COV also prevented symptomatic and asymptomatic infections overall (relative risk reduction, 66.4%). Among symptomatic infected participants, the median time to resolution of symptoms was 2 weeks shorter with REGEN-COV than with placebo (1.2 weeks and 3.2 weeks, respectively), and the duration of a high viral load (>104 copies per milliliter) was shorter (0.4 weeks and 1.3 weeks, respectively). No dose-limiting toxic effects of REGEN-COV were noted.ConclusionsSubcutaneous REGEN-COV prevented symptomatic Covid-19 and asymptomatic SARS-CoV-2 infection in previously uninfected household contacts of infected persons. Among the participants who became infected, REGEN-COV reduced the duration of symptomatic disease and the duration of a high viral load. (Funded by Regeneron Pharmaceuticals and others; ClinicalTrials.gov number, NCT04452318.).Copyright © 2021 Massachusetts Medical Society.

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